一直想自己写一个从HAL层到应用层的Camera例子，android4.0上usb camera用不了 所以决定自己写一个 usb camera和coms原理都是一样的 基本v4l2 只不过源码数据格式不一样而已 下面我们就从HAL层开始
以下是我的代码，先上代码在 一步步说明
fimcgzsd.c
/*
* Android USB Camera zc3xx Library
*
* Copyright (c) 2014 Store information technology guangzhou ltd
* Copyright (c) 2014 hclydao
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License.
*/
#include
#include
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#include
#define LOG_TAG "FimcGzsd"
#define LOGV(...) __android_log_print(ANDROID_LOG_VERBOSE, LOG_TAG, __VA_ARGS__)
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG , LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO , LOG_TAG, __VA_ARGS__)
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN , LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR , LOG_TAG, __VA_ARGS__)
struct fimc_buffer {
unsigned char *start;
size_t length;
};
static int fd = -1;
struct fimc_buffer *buffers=NULL;
struct v4l2_buffer v4l2_buf;
static int bufnum = 1;
static int mwidth,mheight;
/*
*open usb camera device
*/
JNIEXPORT jint JNICALL Java_com_dao_usbcam_Fimcgzsd_open(JNIEnv * env, jclass obj, const jbyteArray devname)
{
jbyte *dev = (jbyte*)(*env)->GetByteArrayElements(env, devname, 0);
fd = open(dev, O_RDWR, 0);
if (fd<0)
{
LOGE("%s ++++ open errorn",dev);
return -1;
}
(*env)->ReleaseByteArrayElements(env, devname, dev, 0);
return fd;
}
/*
* init device
*/
JNIEXPORT jint JNICALL Java_com_dao_usbcam_Fimcgzsd_init(JNIEnv * env, jclass obj, jint width, jint height,jint numbuf)
{
int ret;
int i;
bufnum = numbuf;
mwidth = width;
mheight = height;
struct v4l2_format fmt;
struct v4l2_capability cap;
ret = ioctl(fd, VIDIOC_QUERYCAP, &cap);
if (ret < 0) {
LOGE("%d :VIDIOC_QUERYCAP failedn",__LINE__);
return -1;
}
if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
LOGE("%d : no capture devicesn",__LINE__);
return -1;
}
memset( &fmt, 0, sizeof(fmt));
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB565;
fmt.fmt.pix.width = width;
fmt.fmt.pix.height = height;
if (ioctl(fd, VIDIOC_S_FMT, &fmt) < 0)
{
LOGE("++++%d : set format failedn",__LINE__);
return -1;
}
struct v4l2_requestbuffers req;
req.count = numbuf;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
ret = ioctl(fd, VIDIOC_REQBUFS, &req);
if (ret < 0) {
LOGE("++++%d : VIDIOC_REQBUFS failedn",__LINE__);
return -1;
}
buffers = calloc(req.count, sizeof(*buffers));
if (!buffers) {
LOGE ("++++%d Out of memoryn",__LINE__);
return -1;
}
for(i = 0; i< bufnum; ++i) {
memset(&v4l2_buf, 0, sizeof(v4l2_buf));
v4l2_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
v4l2_buf.memory = V4L2_MEMORY_MMAP;
v4l2_buf.index = i;
ret = ioctl(fd , VIDIOC_QUERYBUF, &v4l2_buf);
if(ret < 0) {
LOGE("+++%d : VIDIOC_QUERYBUF failedn",__LINE__);
return -1;
}
buffers[i].length = v4l2_buf.length;
if ((buffers[i].start = (char *)mmap(0, v4l2_buf.length,
PROT_READ | PROT_WRITE, MAP_SHARED,
fd, v4l2_buf.m.offset)) < 0) {
LOGE("%d : mmap() failed",__LINE__);
return -1;
}
}
return 0;
}
/*
*open usb camera device
*/
JNIEXPORT jint JNICALL Java_com_dao_usbcam_Fimcgzsd_streamon(JNIEnv * env, jclass obj)
{
int i;
int ret;
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
for(i = 0; i< bufnum; ++i) {
memset(&v4l2_buf, 0, sizeof(v4l2_buf));
v4l2_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
v4l2_buf.memory = V4L2_MEMORY_MMAP;
v4l2_buf.index = i;
ret = ioctl(fd, VIDIOC_QBUF, &v4l2_buf);
if (ret < 0) {
LOGE("%d : VIDIOC_QBUF failedn",__LINE__);
return ret;
}
}
ret = ioctl(fd, VIDIOC_STREAMON, &type);
if (ret < 0) {
LOGE("%d : VIDIOC_STREAMON failedn",__LINE__);
return ret;
}
return 0;
}
/*
*get one frame data
*/
JNIEXPORT jint JNICALL Java_com_dao_usbcam_Fimcgzsd_dqbuf(JNIEnv * env, jclass obj,const jbyteArray videodata)
{
int ret;
jbyte *data = (jbyte*)(*env)->GetByteArrayElements(env, videodata, 0);
v4l2_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
v4l2_buf.memory = V4L2_MEMORY_MMAP;
ret = ioctl(fd, VIDIOC_DQBUF, &v4l2_buf);
if (ret < 0) {
LOGE("%s : VIDIOC_DQBUF failed, dropped framen",__func__);
return ret;
}
memcpy(data,buffers[v4l2_buf.index].start,buffers[v4l2_buf.index].length);
(*env)->ReleaseByteArrayElements(env, videodata, data, 0);
return v4l2_buf.index;
}
/*
*put in frame buffer to queue
*/
JNIEXPORT jint JNICALL Java_com_dao_usbcam_Fimcgzsd_qbuf(JNIEnv * env, jclass obj,jint index)
{
int ret;
v4l2_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
v4l2_buf.memory = V4L2_MEMORY_MMAP;
v4l2_buf.index = index;
ret = ioctl(fd, VIDIOC_QBUF, &v4l2_buf);
if (ret < 0) {
LOGE("%s : VIDIOC_QBUF failedn",__func__);
return ret;
}
return 0;
}
/*
*streamoff
*/
JNIEXPORT jint JNICALL Java_com_dao_usbcam_Fimcgzsd_streamoff(JNIEnv * env, jclass obj,jint index)
{
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
int ret;
ret = ioctl(fd, VIDIOC_STREAMOFF, &type);
if (ret < 0) {
LOGE("%s : VIDIOC_STREAMOFF failedn",__func__);
return ret;
}
return 0;
}
/*
*release
*/
JNIEXPORT jint JNICALL Java_com_dao_usbcam_Fimcgzsd_release(JNIEnv * env, jclass obj)
{
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
int ret;
int i;
ret = ioctl(fd, VIDIOC_STREAMOFF, &type);
if (ret < 0) {
LOGE("%s : VIDIOC_STREAMOFF failedn",__func__);
return ret;
}
for (i = 0; i < bufnum; i++) {
ret = munmap(buffers[i].start, buffers[i].length);
if (ret < 0) {
LOGE("%s : munmap failedn",__func__);
return ret;
}
}
free (buffers);
close(fd);
return 0;
}
首先是open这个就不作说明了
第二初始化init函数
ret = ioctl(fd, VIDIOC_QUERYCAP, &cap);
if (ret < 0) {
LOGE("%d :VIDIOC_QUERYCAP failedn",__LINE__);
return -1;
}
if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
LOGE("%d : no capture devicesn",__LINE__);
return -1;
}获取设备相关信息，检查是否支持capture模式
memset( &fmt, 0, sizeof(fmt));
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB565;
fmt.fmt.pix.width = width;
fmt.fmt.pix.height = height;
if (ioctl(fd, VIDIOC_S_FMT, &fmt) < 0)
{
LOGE("++++%d : set format failedn",__LINE__);
return -1;
}设置格式,usb camera获取到的已经是jpeg格式 所以这里设置成RGB565格式
struct v4l2_requestbuffers req;
req.count = numbuf;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
ret = ioctl(fd, VIDIOC_REQBUFS, &req);
if (ret < 0) {
LOGE("++++%d : VIDIOC_REQBUFS failedn",__LINE__);
return -1;
}申请缓冲区,这里申请numbuf个缓冲帧
buffers = calloc(req.count, sizeof(*buffers));
if (!buffers) {
LOGE ("++++%d Out of memoryn",__LINE__);
return -1;
}
for(i = 0; i< bufnum; ++i) {
memset(&v4l2_buf, 0, sizeof(v4l2_buf));
v4l2_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
v4l2_buf.memory = V4L2_MEMORY_MMAP;
v4l2_buf.index = i;
ret = ioctl(fd , VIDIOC_QUERYBUF, &v4l2_buf);
if(ret < 0) {
LOGE("+++%d : VIDIOC_QUERYBUF failedn",__LINE__);
return -1;
}
buffers[i].length = v4l2_buf.length;
if ((buffers[i].start = (char *)mmap(0, v4l2_buf.length,
PROT_READ | PROT_WRITE, MAP_SHARED,
fd, v4l2_buf.m.offset)) < 0) {
LOGE("%d : mmap() failed",__LINE__);
return -1;
}
}映射虚拟内存到物理地址，获取每个缓冲区的物理地址
streamon函数
将缓冲区放入队列并开启数据流
dqbuf函数
获取一帧数据 返回当前缓冲区的序列号
qbuf函数
将指定缓冲区放入队列，获取到某一缓冲区的数据后需要重新将这个缓冲区放入队列
后面两个我就不多说明了
Android.mk文件:
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE_TAGS := eng
LOCAL_SRC_FILES:= fimcgzsd.c
LOCAL_MODULE := libfimcgzsd
LOCAL_LDLIBS := -llog
LOCAL_SHARED_LIBRARIES := libc libcutils
include $(BUILD_SHARED_LIBRARY)
参考博文:https://blog.csdn.net/eastmoon502136/article/details/8190262
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作者：hclydao
https://blog.csdn.net/hclydao
版权没有，但是转载请保留此段声明
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